In horology, and more particularly for watches, mechanical technology is generally used to hold a component, in particular an arbor, in a particular position. It may be held against a stop by an elastic system, particularly when a certain degree of movement is required in the event of a shock. For example, a spring holds an arbor against a stop.
Retention by a preefforted spring is not stable over time: such a spring, which must work with variations in effort due to shocks experienced by the watch, is subject to fatigue and wear, as is every component which is subjected to impact efforts on the stop.
Further, reproducible fabrication of such a spring is difficult. The set of tolerances may also cause great diversity in the value of the preeffort force. Consequently, performance is not stable over time, and the anti-shock effect also deteriorates over the life of the watch.
In short, the main problems encountered with mechanical retention systems that are elastic are the wear of components caused by repeated mechanical effort, and the need to achieve tight tolerances which are therefore expensive.
It therefore remains difficult to ensure the axial retention of a timepiece arbor, with a durable anti-shock mechanism.
EP Patent Application No 2450758 in the name of MONTRES BREGUET SA discloses a method for orientation of a timepiece component made of magnetically permeable or magnetic material comprising two ends, wherein on both sides of said ends, two magnetic fields are created, each attracting said component onto a pole piece, with an unbalance in the intensity of said magnetic fields around said component, in order to create a differential in the forces thereon and to press one of said ends onto a contact surface of one of said pole pieces, and to hold the other end at a distance from the other pole piece. This Application also discloses an electrostatic variant along the same principle. The Application also concerns a magnetic pivot (or an electrostatic variant) comprising such a timepiece component including a guide device with, at a greater air gap distance than the distance of centres between the ends, surfaces of two pole pieces each arranged to be attracted by a magnetic field transmitted by one of the ends, or to generate a magnetic field attracting one of the ends, such that the magnetic forces exerted on the two ends are of different intensity, in order to attract one of the ends into contact with only one of the pole piece surfaces. In that Patent, the main function of the magnets is the radial recentring of the arbor. The two magnets creating magnetic fields on either side of the arbor, each located at one of the ends, are necessary for its operation.
EP Patent Application No 2450759 in the name of MONTRES BREGUET SA discloses mechanical anti-shock devices associated with a magnetic pivot, and in particular a magnetic (or electrostatic) anti-shock device for the protection of a timepiece component mounted to pivot between a first and a second end. It includes, on either side of these ends, on the one hand, means for guiding the pivoting of or means for attracting the first and held resting on a first pole piece, and on the other hand, in proximity to a second pole piece, means for guiding the pivoting of the second end or means for attracting the second end towards the second pole piece, and the means for guiding the pivoting of or means for attracting the first end on the one hand, and the means for guiding the pivoting of or means for attracting the second end on the other hand, are movable along a given direction between stops.
FR Patent 1314364 in the name of HELD discloses a combination of magnets for magnetic suspension of contactless timepiece pivots, with the combination of an annular magnet in a disc pierced right through the centre. It uses magnetic repulsion to obtain suspension, and thus contactless operation. In a first variant, this magnet is radially magnetized, with one pole on the inner generatrices of the hole, and the other pole on the outer generatrices. In a second variant, this magnet is axially magnetized, the two pole areas being distributed over the two circular plane surfaces of the disc, the arbor of the magnetically held and guided movable assembly passing through the centre of the hole in the annular magnet, the arbor being formed by a tube with thin non-magnetic walls containing a hypercoercive material, magnetized in one piece with two poles of opposite signs at the two ends, or in two segments separated by a gap, the opposite ends of the two segments housed inside the protective tube having poles of the same sign, assembled with a fixed disc/magnet, with radial pole axes and poles of the opposite sign assembled with the axially magnetized disc, the gap separating the two segments forming the core of the tubular arbor being similar to the thickness of the disc concerned and placed inside the central hole in the latter, such that the terminal ends of the axial magnet extend slightly inside the hole, the two plane, circular surfaces delimiting the height of the cylinder or magnetized disc.
DE Patent Application 10062065A1 in the name of SIEMENS, WO Patent Application 2011095646A1 in the name of FERREIRO GARCIA RAMON, and JP Patent Application S5659027A in the name of SEIKO, disclose the use of magnetic repulsion to obtain operation in suspension.